1. Field
This application relates to the field of medical handpieces, which include dental handpieces, and in particular to a bearing arrangement for a rotary part of the handpiece.
2. Description of Prior Art
Such medical or dental handpieces serve to drive medical or dental tools using a drive mechanism that has at least one rotary part pivotably (or rotatably) mounted by a bearing arrangement. This part may be, e.g., a tool holder for receiving the tool. In the case of a mechanical drive, it may be a pivotably mounted shaft or in the case of a compressed gas operated turbine drive, it may preferably be a rotor arranged in the head. Medical and dental handpieces may thus have rotary parts pivotably mounted in various areas.
The bearing configuration of the rotary part is formed with at least one bearing which allows rotation of the rotary part with respect to the handpiece. A roller bearing having at least one rolling element arranged between a bearing inner ring and a bearing outer ring is preferably used. The bearing inner ring and bearing outer ring thus each form a raceway for the at least one rolling element.
The tool provided for treatment may be, for example, a rotary tool such as a drill or a tool movable back and forth, e.g., a file for preparation of a root canal.
Such a conventional medical or dental handpiece having a bearing arrangement for a rotary part is known from EP 0 958 791 B1.
Such bearing arrangements known in the prior art for medical or dental handpieces have a rotary part, preferably a bushing for a chucking system or a rotating shaft and at least one roller bearing, preferably a ball bearing. The at least one bearing has a bearing inner ring, a bearing outer ring and at least one rolling element. The at least one roller bearing supports the rotary part to allow it to rotate with respect to the handpiece by the bearing inner ring and the bearing outer ring. The at least one rolling element is supported between the bearing outer ring and an outer side of the bearing inner ring. The inner side of the bearing inner ring supports the rotary part.
One disadvantage of this conventional configuration of the bearing for the rotary part has proven to be the outside diameter of the bearing arrangement, which is determined on the basis of the bearing of the rotary part on the inside of the bearing inner ring. This is determined by the diameter of the several components, namely the rotary part, the bearing inner ring, the at least one rolling element and the bearing outer ring.
Another disadvantage of the conventional configuration is due to the assembly of the bearing part to be supported in the bearing inner ring of the at least one roller bearing. In the prior art, it is common to assemble such roller bearings by pressing them onto the rotary part. However, this assembly results in a negative effect on the roller bearing. By pressing the bearing inner ring onto the rotary part, the roller bearing structure, in particular the desired play of the at least one rolling element with respect to its raceways on the bearing inner ring and on the bearing outer ring, is influenced in a negative manner. Pressing the bearing inner ring onto the rotary part causes the bearing inner ring to widen in the area of the raceways of the at least one rolling element. This leads to a change in the adjustment between the at least one rolling element and its raceways on the bearing rings and thus to an unwanted shortening of the lifetime of the roller bearings.